Masterbatching elastomer blends

ABSTRACT

This invention relates to a process for preparing vulcanizates from blends of incompatible elastomers using a mutual curing system in which the mixing of each elastomeric component of the blend separately, with a carbon black selected to optimize the desired vulcanizate properties of the final blend, is completed prior to blending the resulting black-containing elastomeric mixes into the final mixture. Using this procedure it is possible to prepare vulcanizates that have higher tensile strength than those prepared by mixing simultaneously carbon black and all components of the mixture.

United States Patent [191 Shih-Yuan R0 [111 3,46,371 51 Nov. 5, 1974 MASTERBATCHING ELASTOMER BLENDS [75] Inventor: Rolland Shih-Yuan R0, Wilmington,

Del.

[73] Assignee: E. l. du Pont de Nemours & Co.,

Wilmington, Del.

[22] Filed: Apr. 9, 1973 21 Appl. No.: 349,303

[52] US. Cl 260/4233, 152/330, 260/336 AQ,

260/889, 260/890, 260/4234 [51] Int. Cl C08c 11/18, C08d 9/08 [58] Field of Search 260/889, 415 R [56] References Cited UNITED STATES PATENTS 3,224,985 12/1965 Gladding et al. 260/889 FOREIGN PATENTS OR APPLICATIONS 962,519 7/1964 Great Britain Primary ExaminerMorris Liebman Assistant Examinerl-l. H. Fletcher Attorney, Agent, or Firm-Michael Conner [57] ABSTRACT This invention relates to a process for preparing vulcanizates from blends of incompatible elastomers using a mutual curing system in which the mixing of each elastomeric component of the blend separately. with a carbon black selected to optimize the desired vulcanizate properties of the final blend.'is completed prior to blending the resulting black-containing elastomeric mixes into the final mixture. Using this procedure it is possible to prepare vulcanizates that have higher tensile strength than those prepared by mixing simultaneously carbon black and all components of the mixture.

5 Claims, N0 Drawings 1 MASTERBATCHING ELASTOMER BLENDS BACKGROUND OF THEINVENTION It has been known for a considerable length of time that one may blend'various elastomers to achieve a resulting blend whose characteristics reflect the contribution of the several elements of the blend. For instance, if the ozone resistance of one elastomer is superior to another elastomer and they are blended in roughly equal proportions the resulting blend will have ozone resistance which would be intermediate between that of the two elastomers.

A problem which has been encountered when preparing blends of various elastomers is that certain physical properties, such as tensile strength, will be substantially inferior to that of the elastomer having the higher tensile strength in the blend. That is to say, the property will usually be well below an average of the several tensile strengths attributable to the components of the blend.

Typically, each elastomer in such prior art blends is masterbatched with the same filler or carbon black. This may be done by: l) masterbatching each elastomer with the same filler and then blending the masterbatches; 2) masterbatching each elastomer with the same mixture of fillers and blending the masterbatch'es; and 3) mixing one or more fillers with the combined elastomers at the same time.

It is thought that these procedures lead to unequal reinforcement-of the elastomer phases by the fillers since carbon blacks tend to demonstrate varying degrees of affinity toward the various elastomers of the mixture. Because of this variance in affinity, the properties of the various elastomers, e.g. tensile strength, ozone resistance, are not all maximized and the resulting properties of the entire blend will reflect at best a proportionate reduction.

Thus a method is needed for preparing a homogeneous carbon-black containing blend of elastomers in which the properties of the blend are maximized by adding to the individual elastomers a carbon black which maximizes the desired vulcanizate properties.

According to this invention it has unexpectedly been found that if one adds to the individual elastomeric polymers which are to be used in an elastomeric blend, prior to blending, a carbon black which optimizes the desired properties of the elastomer, e.g. tensile properties, and then blends the several carbon blackcontaining elastomers prior to curing, following the cure a blended elastomer is recovered which has optimum physical properties, e.g., tensile properties, in addition to the other advantages obtained by blending the particular elastomers.

This technique may be used with any blend of two or more elastomers but in a preferred embodiment of the instant invention, which typifies the improvement thereof, chloroprene polymer which is a common name for synthetic rubber made by polymerization of 2- chloro-l,3-butadiene, may be blended with a polymer of ethylene, propylene and at least one non-conjugated diene (EPDM).

The tensile properties of vulcanized EPDM are optimized by the addition of a high reinforcing carbon black since the polymer has low gum tensile strength; chloroprene polymer, conversely, requires a less reinforcing carbon black to achieve comparable tensile properties to that of EPDM because the chloroprene polymer has relatively high gum tensile strength. Such a black is referred to as a semi-reinforcing black.

By high reinforcing carbon black is meant a carbon black having the following characteristics: small particle size, about 200-300 'A diameter and large surface area, about -130 sq. meters/gm. High reinforcing blacks are made generally by the well known chemical process or oil furnace process. A low reinforcing black has the following general characteristics: large particle size, about 1,500-5,000 A diameter, and small surface area, about 5-20 sq. meters/gm. Low reinforcing blacks are made generally by the well known thermal process. The neoprene is reinforced with a semireinforcing black of intermediate particle size, about 500-900 A diameter, and about 21-40 sq. meters/gm. area. The blacks are blended into the elastomers by a variety of well known means such as mastication on a rubber mill or in an internal mixer. Additional ingredients are added in the same manner. Thetwo elastomerblack mixes are then combined using the same type of mixing operations. The resulting elastomeric mixture is then cured by conventional techniques and a vulcanizate recovered which has improved tensile strength and often improved tear strength.

DETAILED DESCRIPTION The instant invention is applicable to any blends of at least two elastomers of different gum tensile properties; it should be emphasized, however, that it is preferred to utilize the invention with a blend of a chloroprene polymer and a linear branched polymer of ethylene, propylene and at least one non-conjugated diene (EPDM). Other blends which may be improved by the instant invention include: chloroprene polymer/modified EPDM such as allylically brominated EPDM and chloroprene polymer/butyl rubber.

The invention will, however, be discussed in terms of the previously mentioned chloroprene polymer-EPDM blend since it typifies the improvement which may be achieved.

In more detail, the chloroprene polymer having a Mooney viscosity (ML l+4/250F) range of about 20 to 150, preferably 40 to 100, is combined with a semireinforcing carbon black. Usefulchloroprene polymers are prepared using the procedures of the following U.S.

Pat. Nos. 2,494,087; 3,105,055; 3,397,173 which are herein incorporated by reference. The black is added in the form of particles having an average size of about 500-900 A diameter and in the amount of about 10 to 200 parts of carbon black parts per one hundred rubber, preferably about 50-100, by adding it directly to a polymer banded on a rubber mill or by adding with a polymer in an internal mixer. Typical carbon blacks which may be utilized include the following: medium thermal and semireinforcing furnace blacks. The other elastomer which is to beblended with the chloroprene polymer is composed of ethylene, propylene and at least one nonconjugated diene. Typically, the elastomer contains 30-75 weight percent ethylene, about 20-60 weight propylene and up to 10 weight percent of at least one nonconjugated diene. The nonconjugated diene can be a cyclic diene such as dicyclopentadiene, cyclooctadiene, 5-alkenyl-substituted 2-norbornenes (e.g. 5-propenyl-2-norbornene), and S-alkylidene-Z- 'norbornenes (e.g. 5-ethylidene-2-norbornene). Of the (4) Sulfur be utilized and it 1s preferred that the (11610 contain Zinc dimethyldithiocarbamm 25 about 6-22 carbon atoms. Representative dienes are Zincbenzothiazyl sulfide. 0.5 1,4-hexadiene, 1,5-octadiene, 9-ethyl-l ,9- (5) Sulfur 2 5 undecadiene, l2-ethyl-l ,Z-tetradecadiene and zi dimethyldithiocarbamate 1.75 1- e Tetramethylthiuram disulfide 1.75 15 6th? 1,15 hgptad cadlevne 5 Zinc benzothiazyl sulfide 0.5 Particularly preferred are terpolymers of ethylene, (6) T t h Mud 1 B ramet iuram lSU l e propylene and open-chain noncon ugated diene having Dipemameythylenethimm tetrasulfide 3 both terminal and internal unsaturation. Such dlenes 2-Mgggggtghggg1hlag9je 2.22

are known in the art as monoreactive dienes. Under polymerization conditions the terminal unsaturation of 10 The amount of curing agent may be varled within the monoreactive diene copolymerizes with ethylene ranges Obvious to one Skilled in the and propylene monomers to form a terpolymer having Suitable, alltioxidahts which may h added P an essentially saturated backbone. Terpolymers of ethhohc ahtloxlflams Such as y P'Ph Y ylene, propylene'and 1,4-hexadiene are especially pre- PhehOl; y 'p' and a anhoxldams ferred. The ethylene-propylene-diene terpolymers can Such as 'ph y p y amine and 'P y be prepared by copolymerization of the monomers in p y aminean inert solvent using a coordination catalyst system The resulting Vulcanlleq blelld would be useful f such as diisobutylaluminum chloride and vanadium oxthe f g Purposes: tll'e Slde Walls, foams, Wll'e ychlori'de. Details of their preparation are given in US. Coating and g- Pat. Nos. 2,933,480; 3,000,086; 3,260,708; 3,423,028; In the following p e all Parts and Proportions 3,635,919 and 3,637,616 all of which are herein incorare y Weightporated by reference. A high reinforcing carbon black I; a s then added to the resulting polymer bymeansof mix- EXAMPLE 1 mg in an internal mixer or on a rubber mill. Particularly preferred high reinforcing blacks are the following: one hundred Parts of an ahfylmercaptah modlfieh super abrasion furnace black and high abrasion furnace polychloroprene rubber was mlxed on a two You black. 7 I 7 with 0.5 part stearic acid, 2 parts phenyl-oz- The blends may Contain parts of one compo naphthylamine, 4partsmagnesiumox1de, 58 parts SRF em and parts of the other Proportions may be carbon black, 10 parts of an aromatic oil sold as Sunvaried in accordance with the desired properties of the f 790 011 by S 011 parts i Oxide parts blend which is being produced I VJ b s(octadecyl 1sopr 0pyl)th1uram dlsulfide, 3 parts Mme-fir dipentamethylenethluram tetrasulfide and 1 part The Tesuhlhg masterbatches cohtamlhg the most 2-mercaptobenzothiazole. Test specimens were cured sirable carbon blacks, are then blended together on a in a press for 30 min at 1520C Samples were tested by mill or in an internal mixer at a temperature of about standard methods (ASTM D4172) One'hundred parts 25-150C by means well known in the art. Prior to or of EPDM, an ethylene/32 wt percent propylene/4 wt after blending curing agents, processing aids and antipercent l,4 hexadiene terpolymer of Mooney viscosity oxldams may be adflede 7 (ML 1+4, 250F.) 58, was compounded with the same The blended elastomers or elements of the blend are 40 ingredients and cured in the same manner as described then cured. Curing may. take place by any conventional above. 50 parts of the polychloroprene and 50 parts of technique. Typically, curing will take place at a temthe EPDM were mixed thoroughly on a two roll mill perature of 140-200C, preferably 150180C for a and then compounded with the same ingredients and period of about 5-120 min., preferably 20-40 min. The cured as described above. Tensile properties of all following combinations of curing agents are examples three samples are shown in Table l.

' Table l Tensile Properties Polychloroprene EPDM /50 Blend Tensile at Break, psi. 2850 1850 2330 Modulus at 100% Elongation, psi. 600 350 500 Elongation at Break, 320 300 340 This example illustrates that the vulcanizate of the raw polymer mill blend has tensile strength intermediate between those of the two individual components, but substantially inferior to the component of higher tensile strength.

60 EXAMPLE 2 of systems useful for the vulcanization of EPDM rubberand chloroprene polymer blends:

( I Sulfur Tctramethylthiurum monosulfide Z-Mercaptobenzothiazole cumin (2) Sulfur Tetramethylthiuram disulfide Dipentamethylenethiuram tetrasulfide Z-Mercaptobenzothiazole (3) Sulfur Tetramethylthiuram disulfide Dipentamethylenethiuram tetrasulfide Tellurium diethyldithiocarbamate Z-Mercaptobenzothiazole This example illustrates that no improvement in the tensile strength is obtained with blends of separate masterbatches reinforced with the same carbon black.

One of the major advantages of polychloroprene/EPDM blends is that the blends exhibit improved ozone resistance as compared to 100 percent polychloroprene. For example, the above polychloroprene vul- EXAMPLE 3 5 canizate developed severe cracking after about 20 hrs. Polychloroprene and EPDM masterbatches were exposure to 3 ppm ozone, while the 50/50 blend only prepared using the ingredients shown in Table 11 by the showed trace signs of cracks under a microscope after procedure of Example 1. The tensile properties of their 178 hrs. exposure under the same conditions. Using the vulcanizates after curing and testing as in Example 1 are blending technique described in this example. blend also shown in Table ll. A blend of the two masterbatcompositions with g ozone resistance can be ches was th;.. mixed on the mill to give a resulting tained without detrimental sacrifice of the tensile stock with the same polymer ratio (SO/50) as the blend Strengthin Table 1.

Table I1 Compounding Recipes for the Masterbatchesa A. Polychloroprene of Example 1 100 Stearic acid 0.5 Phenyl-wnaphthylamine 2 Magnesium oxide 4 SRF carbon black 58 Sundex 790 Oil 10 Zinc oxide 5 Tetramethylthiuram disulfide l Dipentamethylenethiuram tetrasulfide 3 2-Mereaptobenzothiazole 1 B. EPDM of Example I 100 HAF carbon black 60 Sundex 790 Oil Zinc oxide 5 Tetramethylthiuram disulfide l Dipentamethylenethiuram tetrasult'lde 3 Z-Mercaptobenzothiazole 1 Press cure: min. at 150C.

Tensile Properties Polychloroprene EPDM /50 Blend Tensile at break, psi. 2870 2650 2760 Modulus at elongation, psi. 500 460 410 Elongation at break, 440 310 420 This example illustrates the improvement in tensile EXAMPLE 4 strength obtained with blends of optimumly reinforced masterbatches wherein two different elastomers are separately compounded with two different carbon blacks.

The compounding recipes and the tensile properties are shown in Table III. The compounding, vulcanization, and testing procedures were those of Example 3.

Table III B. EPDM of Example 1 HAF carbon black Sundex 790 Oil Zinc oxide Sulfur Tetramethylthiuram disulfide 2-Benzothiazolyl disulfide Zinc salt of dibutyldithiocarbamate Press cure: 30 min. at 152C.

Tensile Properties l Polychloroprene EPDM 50/50 Blend Tensile at break, psi. Modulus at 100% elongation, psi. Elongation at break,

This example illustrates further that improvement in tensile strength can be obtained with blends of optimumly reinforced masterbatches as in Example 3 but using a different curing system.

EXAMPLE 6 The ingredients listed in Table IV were processed as described in Example'3. Testing results are also shown in the table.

Table IV Compounding Recipes A. Polychloroprene of Example 1 100 HAF carbon black Sundex 790 Oil Phenyl-a-naphthylamine Magnesium oxide Zinc oxide Tetramethylthiuram disulfide Dipentamethylenethiuram tetrasulfide Z-mercaptobenzothiazole 50 20 Stearic acid 0.5

B. EPDM of Example 1 100 HAF carbon black 70 Sundex 790 Oil Zinc oxide 5 Tetramethylthiuram disulfide l Dipentamethylenethiuram tetrasulfide 3 Z-mercaptobenzothiazole l Tensile Properties Polychloroprene EPDM 50/50/Blend Tensile at break. psi. 3320 3070 2880 Modulus at [00% elongation, psi. 480 380 450 Elongation at break 480 480 450 EXAMPLE 5 This example illustrates that as compared to the raw polymer mill blends little or no improvement in tensile strength is obtained when all the compounding mgr-ed1- This example illustrates that improvement in tensile strength of a blend can also be obtained through balanced reinforcement of two polymers by separately masterbatching with the same carbon black and plasticizing oil but at different loadings.

Polychloroprene has a higher affinity toward the carbon black and is more highly reinforced than EPDM. Therefore, a lower loading of carbon black is polychloroprene than that in the EPDM is necessary to achieve balanced reinforcement in both phases in the blend.

EXAMPLE 7 ents including the two polymers are mixed at the same time. 1 The compounding recipes and the tensile properties Table V Compounding Recipes A. Polychloroprene of Example I 100 Stearic acid 0.5 Phenyl-a-naphthylamine 2 Magnesium oxide 4 SRF carbon black 58 Sundex 790 Oil l0 Zinc oxide 5 Ethylene thiourea 0.75

' Tetramethylthiuram disulfide 0.75

B. Allylically brominated EPDM 100 Stearic acid 0.5 Magnesium oxide 4 HAF carbon black Sundex 790 Oil 15 Zinc oxide 5 Ethylene thiourea Press cure: 30 min. at l52C.

Table Y-Contintred Tensile Properties at 100C.

of the vulcanizates are shown in Table V. The procedures used were those of Example 3. I

This example illustrates that the high tensile strength of a blend of polychloroprene and allylicallybrominated EPDM is obtained with the same blending technique as described in Example 3.

EXAMPLE 8 What is claimed is: l. A process for blending a chloroprene elastomeric polymer and an elastomeric polymer or its allylically brominated derivative comprising ethylene, propylene and at least one non-conjugated diene which consists essentially of separately adding to said chloroprene polymer a semi-reinforcing black, and adding a high reinforcing black to the ethylene-containing polymer, blending the two black containing elastomers in the uncured state, curing the elastomers in the presence of one or more curing agents compatible with the elastomers in the blend and recovering a blend of elastomers having at least one optimized property.

2. The process of claim 1 wherein said nonconjugated diene is 1,4-hexadiene.

3. The process of claim 1 wherein said blending takes place in a rubber mill or an internal mixer.

4. The process of claim 1 wherein the high reinforcing black is selected from super abrasion furnace black and high abrasion furnace black.

5. The process of claim 4 wherein the semireinforcing black is selected from medium thermal and semi-reinforcing furnace black.

l= l l 

1. A PROCESS FOR BLENDING A CHLOROPRENE ELASTOMERIC POLYMER AND AN ELASTOMERIC POLYMER ITS ALLYLICALLY BROMINATED DERIVATIVE COMPRISING ETHYLENE, PROPYLENE AND AT LEAST ONE NON-CONJUGATED DIENE WHICH CONSISTS ESSENTIALLY OF SEPARATELY ADDING TO SAID CHLOROPRENE POLYMER A SEMI-REINFORCING BLACK, AND ADDING A HIGH REINFORCING BLACK TO THE ETHYLENE CONTAINING POLYMER, BLENDING THE TWO BLACK CONTAINING ELASTOMERS IN THE UNCURED STATE, CURING THE ELASTOMERS IN THE PRESENCE OF ONE OR MORE CURING AGENTS COMPATIBLE WITH THE ELASTOMERS IN THE BLEND AND RECOVERING A BLEND OF LEASTOMERS HAVING AT LEAST ONE OPTIMIZED PROPERTY.
 2. The process of claim 1 wherein said non-conjugated diene is 1,4-hexadiene.
 3. The process of claim 1 wherein said blending takes place in a rubber mill or an internal mixer.
 4. The process of claim 1 wherein the high reinforcing black is selected from super abrasion furnace black and high abrasion furnace black.
 5. The process of claim 4 wherein the semi-reinforcing black is selected from medium thermal and semi-reinforcing furnace black. 